Buying a compressor

[Hoosier]

I get ~3.1 cfm out of my Alkins. Definately not 3.5, but more than 2.8

With compressors this small, using the condensate drains seems to have a significant influence on your pumping rate. I use a timer set at 17 mins and vent just enough to see little moisture. Helps to be in a cool climate.

2 fans help keep them heads cool.

I am not sure which factor really affects on my baby.. Mine is AD model, so I just leave it alone. I added LF appliance, so it might be another factor though.

Do you think that an addtional stack is decreasing an output rate?

BTW, how do you read the timer on the compressor? It isn't a time unit.....

 

[rjack321]

The autodrains supposedly bleed off more gas than manual, since I shut 'em down when they are dryish and the AD goes for 10 seconds or whatever.

Unless you have a leak or are continually bleeding down your 2nd, 3rd, etc. stacks they shouldn't matter. I leave my second filter pressurized to 1900 (the backpressure reg setting).

The only time I bleed it down is when I'm doing:
1) a filter change
or
2) been pumping air and want to CB nitrox or trimix.

There's 13cf of gas in my second chamber and I don't want to "contaminate" a tank of something else, throwing off the O2%age.

 

[pescador775]

Thanks, guys, for the info. I have no axe to grind. Well, originally, I became interested in the subject years ago, and was convinced I could DIY a compressor with better performance than the factory made product. That was easy to do in those days because the only portable around was the Bauer Purus. Later, the matter came up again and I realized how difficult it was to talk to the subject in an intelligent manner. Obtaining data on the branded machines is more difficult than might be expected. For example, until a year ago, the Alkin was advertised as 3.5 cfm @ 900 rpm; now, 3.5 cfm @ 1200 rpm. Huh? In 2004, Genesis tested his new Alkin, the 900 rpm type, and gave a result of 3 cfm. MaxAir stated that the Coltri would fill an S80 in 28 minutes. Bauer once indicated 24 minutes for the S80. I tested a Bauer Utilus 10 (Junior type) at 24 minutes hot fill. Add to that a couple minutes to obtain true SCFM at 72F and get 26 minutes to fill a 77.4 cf tank. That gives a result close to 3 cfm. I saw a paintball style Oceanus rated 3.5 cfm vs the usual 4.0. There was a plate on the side with this rating printed on it. Now, Bauer Kompressoren sells the same compressors to divers and paintballers, same ratings. Yet, I suspect that Bauer/Norfolk may be doing something different, like playing with the engine pulley sizes, installing smaller shieves; perhaps, if so because paintballers jam higher pressures and may run hotter. It's a bit confusing and each time I hang up the phone on this subject something comes back to nag. That's unfortunate because as consumers, most would not appreciate buying a product whose performance could not be verified at point of sale. Who would like to buy a lawn mower with 48 inch cut only to discover it was actually 42 inches? Well, that sort of thing.

 

[Hoosier]

I have been wondering my output rate.... I might check any leak again...

It is an endless maintenance... Sigh~~~~

 

[Dan Gibson]

I can say that I only get about 2.6 cfm with my Alkin. My O2 flowmeter setting supports these numbers as well and I am almost always spot on with the mix. Now it might be slightly more as you can't read the flow meter that closely and I might open the drains a tad too long, but the output is no where near the rated 3.5 cfm and it isn't close to 3 cfm with my compressor.

btw, I thought Karl's compressor was 1200 rpm which is the same as mine. I have never seen it rated at 900 rpm, but I could be wrong.

Thanks, guys, for the info. I have no axe to grind. Well, originally, I became interested in the subject years ago, and was convinced I could DIY a compressor with better performance than the factory made product. That was easy to do in those days because the only portable around was the Bauer Purus. Later, the matter came up again and I realized how difficult it was to talk to the subject in an intelligent manner. Obtaining data on the branded machines is more difficult than might be expected. For example, until a year ago, the Alkin was advertised as 3.5 cfm @ 900 rpm; now, 3.5 cfm @ 1200 rpm. Huh? In 2004, Genesis tested his new Alkin, the 900 rpm type, and gave a result of 3 cfm. MaxAir stated that the Coltri would fill an S80 in 28 minutes. Bauer once indicated 24 minutes for the S80. I tested a Bauer Utilus 10 (Junior type) at 24 minutes hot fill. Add to that a couple minutes to obtain true SCFM at 72F and get 26 minutes to fill a 77.4 cf tank. That gives a result close to 3 cfm. I saw a paintball style Oceanus rated 3.5 cfm vs the usual 4.0. There was a plate on the side with this rating printed on it. Now, Bauer Kompressoren sells the same compressors to divers and paintballers, same ratings. Yet, I suspect that Bauer/Norfolk may be doing something different, like playing with the engine pulley sizes, installing smaller shieves; perhaps, if so because paintballers jam higher pressures and may run hotter. It's a bit confusing and each time I hang up the phone on this subject something comes back to nag. That's unfortunate because as consumers, most would not appreciate buying a product whose performance could not be verified at point of sale. Who would like to buy a lawn mower with 48 inch cut only to discover it was actually 42 inches? Well, that sort of thing.

 

[rjack321]

My O2 flow is 'only' 12L/min which theoretically shouldn't be enough for 32% (but it works). I have assumed the guage or orifice is off a bit. My nurse wife says the med O2 flow gauges are notoriously unreliable in the hospital.

So instead, I have timed filling double 100s and get between 3.0 and 3.1 cfm out of my Alkins. A bit less in hot summertime (2.9 or so). More in winter, maybe 3.2 when its 40-45F out.

I bought it 12/2005 and have no idea of its speed. I have #10 wires feeding the panel, shouldn't be much voltage drop (although I have never checked).

 

[Dan Gibson]

My Alkin was purchased back in February 2004.

Mine O2 flow is somewhere near 10.6 lpm if I recall corectly. It's been a couple of months since my last continuous blend (sounds kind of like an AA meeting ) I also compare this info to my fill times.

Sometime I should do a run where I just don,t dump until I fill an AL 40 or 80 from empty to full with the filter already up to pressure.

I have some new flow meters with a larger scale to work with that I will install soon. Maybe this will help nail down the numbers a little better, but I'm very doubtful of 3.0 cfm

My O2 flow is 'only' 12L/min which theoretically shouldn't be enough for 32% (but it works). I have assumed the guage or orifice is off a bit. My nurse wife says the med O2 flow gauges are notoriously unreliable in the hospital.

So instead, I have timed filling double 100s and get between 3.0 and 3.1 cfm out of my Alkins. A bit less in hot summertime (2.9 or so). More in winter, maybe 3.2 when its 40-45F out.

I bought it 12/2005 and have no idea of its speed. I have #10 wires feeding the panel, shouldn't be much voltage drop (although I have never checked).

 

[Dan Gibson]

If I had to do it all over, I would have gotten the W32 Mariner since I have very little patience.

My O2 flow is 'only' 12L/min which theoretically shouldn't be enough for 32% (but it works). I have assumed the guage or orifice is off a bit. My nurse wife says the med O2 flow gauges are notoriously unreliable in the hospital.

So instead, I have timed filling double 100s and get between 3.0 and 3.1 cfm out of my Alkins. A bit less in hot summertime (2.9 or so). More in winter, maybe 3.2 when its 40-45F out.

I bought it 12/2005 and have no idea of its speed. I have #10 wires feeding the panel, shouldn't be much voltage drop (although I have never checked).

 

[pescador775]

Dan, how the measurement is done depends on the premise, that is "what method represents the performance of a compressor?" My objective is to replicate manufacturers and government tests, to normalize results with the intention of obtaining output numbers for the block and to delete the effect of filling condensators and filters. Thus, I don't use flowmeters to determine compressor output because results will vary with the size of the filter set. Well, the test could be done at the output pipe coming off the block and produce a valid result. Test procedures specified by governments always involve the filling of a standard size test bottle, sometimes 1 liter @ 200 bar, sometimes more. The method for testing is to fire up the compressor and run up the pressure in the filter set to 200 bar, open the valve on the bottle and time the run to 200 bar. The result is obtained by dividing the capacity of the bottle (200 liters, etc) by the fill time.

I understand the concerns of continuous flow blending and how real time numbers are needed for this technique. However, comparisons of the numbers in this context can give different results from that of the manufacturers claims and other test results.

 

[rjack321]

Roughly, this is how I have been calculating, er guessing, my output.

The larger the cylinder your filling, the less having your condensor or filters muck with the precision of the timing. Bank bottles being ideal for estimating rate, doubles a good second choice. A single 80 is harder to accurately measure IMO.